Editors know that English spelling preferences differ from the Americas to Europe, and even differ within the Americas. MS Word is ready to help, with at least three options for English spellcheck dictionaries in the Language settings.
Most recently, we find options for Canadian, US, UK, and Australian spellings in Word for Mac. 
A full 18 English options are available in Word for Windows.
Setting the language preference is easy: on the Review ribbon, click the Language icon, then press E to skip to the English section of the list. Select the preferred English for the document, then click Ok. You can even tell word to set that as the Default by pressing that button before you press Ok.
In Word for Windows, the 18 English options include (beyond those shown in the images above) Jamaica, Malaysia, New Zealand, Philippines, Singapore, South Africa, Trinidad and Tobago, and Zimbabwe.
Troubleshooting
- Select the entire document (cmd + A, or ctrl + A on Windows) before entering the settings in order to set the language for the whole document rather than just the paragraph in which the cursor is currently placed.
- If the language choice won’t “stick”, check the Style settings. Not only can a style specify aspects of the font, it can also set the language. Modify the style to match your preference. Also be sure that the style is set to “check spelling and grammar” rather than to “do not check.”
- Language settings are document specific. The spellcheck preference needs to be set for each document.
- Some sections of text may be set (either manually or via Styles) to not check the spelling and grammar there. This is useful when we want Word to skip lengthy quotes or passages in another language but problematic when set by mistake. Find that option either in the Style settings or when selecting the language for that particular paragraph.
